Seasonal Climate Outlook Message for August to November 2003

The bottom line

Climate Outlook Dave McRae Qld Dept of Primary Industries 13/08/03

Rainfall probabilities for August to October across most of the southern two thirds of Queensland have lifted to around 50-80%. Rainfall probabilities across the rest of the state though are patchy with lower probabilities (eg 30-40%) persisting across much of the far west of the state.

While rainfall probabilities for much of Queensland for the August to October have improved, we remain circumspect about the outlook beyond that. This is important is years such as this one where the Pacific Ocean remains in a fairly volatile state and the SOI continues to swing erratically. So while the current seasonal outlook has improved there remains a strong need to get the latest outlook on a regular basis in years such as this one.

For there to be increased confidence in the longer term outlook (eg through to summer) SOI monthly values will need to be become more positive over the coming months. The 30day average of the SOI as of the 13th August was plus 0.1.

While the current sea surface temperature (SST) pattern is an improvement over the last 12 months, SST patterns have not changed significantly enough to guarantee an immediate large improvement in overall conditions throughout Queensland. Some concern has also been raised about some rewarming of subsurface temperatures throughout the central Pacific. As well, the preferred easterlies and south east trade winds have been weaker than average.

Due to these ongoing changes the chance of an El Nino regenerating while remaining low has increased marginally. However a late winter or spring transition into an El Nino sea temperature pattern is quite unusual.

As usual much interest is being shown in the next passage of the MJO (40day wave). The MJO is simply a band of low atmospheric pressure originating off the east coast of central Africa travelling eastward across the Indian Ocean and northern Australia roughly every 30 to 50 days. While it is a tropical phenomenon, it appears to indicate the timing of potential rainfall events (but unfortunately not rainfall amounts) over central and southern Queensland.

The last passage of the MJO (40day wave) influenced Queenslands weather around mid July producing some generally useful falls across the state. As it's timing appears to have shifted to approximately 50days it is next expected to influence our weather in late August or early September.